the usual apparatus for pumping well fluids from a producing earth formation through a tubing which extends from the surface to the formation penetrated by the well includes a sub-surface pump whose barrel is connected to the lower end of the tubing and has a plunger or "traveling valve" which is reciprocated in the pump barrel by a sucker rod string. Such sucker rod string normally comprises a plurality of serially connected sucker rods of relatively great lengths, twenty-five or thirty feet long, and having shanks of relatively small diameter, and a stabilizer bar or rod of much shorter length, for example two to five feet, connected to the bottom end of the lowermost sucker rod. Such stabilizer rod is of greater rigidity then the sucker rods not only because of its much shorter length, but also because of the greater diameter of its shake as compared to that of the shanks of the sucker rods, for example, one inch compared to three quarters of an inch. The bottom end of the stabilizer rod is connected either directly to the "traveling valve" and its top end may be connected to the bottom end of the lowermost sucker rod or, if sinker rods, which are used to accelerate the rod strings downward movement during the down stroke of the reciprocal pumping cycle, are in the lowermost position in the string, to the lowermost sinker rod.
The top rod of the sucker rod string is connected to a motor driven means for alternately pulling the sucker rod string upwardly and then allowing the string to be moved downwardly gravity.
Since the weight of the sucker rod string, increased by the weight of the sinker areas if they are used, provides the force necessary to cause well fluids to flow upwardly through the tubing, if resistance to the downward movement of the traveling valve and to the sucker rod string by the upwardly flowing well fluids is great, especially past such obstructions to fluid flow as the connector means connecting adjacent ends of adjacent rods, the sucker rod string will move downwardly relatively slowly thus reducing the rate of production of he well fluids. The connector means decreases the flow space area between the rod and the tubing and also therefore increases the turbulence of the well fluids flowing therepast as well as increasing vibrations imparted to the string. In addition, if the traveling valve and lower end portions of the rod string offer a relatively great resistance to downward movement of the rod string, the weight of upper portions of the rod sting may cause the lowermost portions of the string to be placed under great compression loads which tend to cause such lower portions to bend and buckle and their connector means to be moved with great force against the internal surfaces of the tubing.
Such vibrational and longitudinal sliding frictional contact of the lower portion of the rod string with the tubing thus caused results in damage to and failure of the rods and also of the portions of the tubing engaged thereby. The thicker shank stabilizer rods usually provided with centralizers are used to decrease such contact, damage and failure and help hold the traveling valve properly aligned in the pump barrel.
The conventional API standard sucker rods and stabilizer bars or rods have connector means, such as threaded pins on the opposite ends of the rods and annular coupling stop shoulder, whose diameters vary in a set manner in accordance with the diameters of the shanks of the rods. For example, conventional sucker and stabilizer rods whose shanks are one inch in diameter have connector pins having an outside diameter of 1.3735 inches and pin or stop shoulders, which limit movement of the pins into couplings, that are 2.0 inches in diameter while rods which have three quarter of an inch diameter shanks have pins which have an outside diameter of 1.061 inches and in shoulders 1.5 inches in diameter. It will be seen therefore that the cross-sectional area of the pin stop shoulders of the standard three quarter inch diameter shank rod is only 1.777 square inches while that of the standard one inch shank rod is 3.1416 square inches. The cross sectional area of a flow passage between the connector means of a standard three quarter inch shanks rod and a standard well tubing, for example, having an internal diameter of 2.441 inches is therefore 2.930 square inches while that between the connector means of a standard one inch shank rod and the same tubing is only 1.555 square inches.
If a sucker rod string is provided, as has been the practice, with a stabilizer rod of greater strength and rigidity due to the greater diameter of its shank as compared to that of the shanks of the sucker rods of the strings, for example, one inch versus three quarters of an inch, the restriction of the flow passage in the tubing at the connector means at the opposite ends of the stabilizer rod are much greater than those of the locations of the connector means of the sucker rods. In addition, special adaptor or connector means must be provided to connect the connector pins of the stabilizer rod to the different sized pins of the sucker rods and to the sinker bar or pump travelling valve.
It is desirable that a stabilizer bar or rod be provided whose connector means, the pins and stop shoulders at its opposite ends, be of the same diameter as those of the other members of the well apparatus between and to which it is connected, even through its shank is of greater diameter than the shanks of such other members, in order that connection of such stabilizer or rod in a sucker rod sting not result in a decrease in the area of the flow passage between the tubing, in which the sucker rod string is reciprocally movable, and the string at the locations of the opposite ends of the stabilizer bar.